This invention relates to a dome speaker.
As shown in FIGS. 12 and 13 of the accompanying drawings, the dome speaker of the prior art generally comprises a ring magnet 11', a center pole 12', a front plate 13', a back plate 14', a diaphragm 15', a voice coil 1' mounted on a voice coil bobbin 1a' secured to the outer periphery of the diaphragm 15' and disposed in a magnetic space between the center pole 12' and the front plate 13', and an edge 5' supporting the diaphragm 15'. The voice coil 1' is energized with audio currents to activate the diaphragm 15' whereby sound waves are radiated.
The diaphragm 15' is in most cases formed of hard metal such as duralumin and into dome shape as seen from FIGS. 12 and 13. The hard diaphragm of this type involves small mechaical internal loss in the diaphragm material in a frequency range higher than a piston vibration range. Therefore, vibrating energy conducted from peripheries of the diaphragm and the vibrating energy reverberated from the center of the diaphragm interface with each other thereby to create a nodal line adjacent the outer peripheries of the diaphragm. Since the vibrations of the diaphragm are in opposite phases across the nodal line, a dip is formed in the anti-resonance frequency in frequency characteristics, which dip is flanked by peaks in higher and lower frequency ranges. This deteriorates the frequency characteristics and transient characteristics to the deteriment of aural quality.
A further example of dome speaker, so-called soft dome speaker, employs for the diaphragm a soft material involving a great internal loss. Although this type of diaphragm is relatively free from resonance and anti-resonance, vibrating energy cannot easily be conducted through the diaphragm because of its large mass. Therefore, this type of speaker has the disadvantage of very poor efficiency of energy conversion.